Pulmonary Function Tests - Scharf

Question 1

Modules of pulmonary function test

Answer 1

Module 1: Spirometry

Our ECG
If you only had one on a desert island
Bronchodilator response often ordered
Defines “asthmatic physiology” or “reversibility” or the extent to which airflow obstruction is due to smooth muscle tone

Module 2: Lung volumes: gas dilution or body plethysmography

Module 3: Gas exchange
CO diffusion capacity (DCO)
Arterial Blood Gases
Shunt studies – give 100% oxygen

Module 4: Bronchial challenge testing
To mediators of airway obstruction (methacholine-ACh analogue, histamine, others. Checks bronchoresponse)
To exercise
Specific

Module 5: simple tests of respiratory muscle function- Max inspiratory/expiratory

Module 6: Fancy tests (not so commonly ordered)
Pressure volume curve of the lung
Testing small airway function
Co2/O2 response curves
Complicated tests of respiratory muscle function

Question 2

What is the Forced Volume Capacity (FVC)?

Answer 2

TLC-RV, max expelled during forced spirometry

Question 3

What is FEV1?

Answer 3

Amount expelled from TLC during the first second of forced spirometry.

Question 4

What is the lower limit of normal for predictions of FEV1?

What are the measures for severity of ventilatory defect (mild, moderate, severe)?

Answer 4

80%, lower for older patients and other factors.

60-80% mild

40-60% moderate

<40% severe

Question 5

What are the measurements of obstructive vs restrictive defect

Answer 5

FEV1/FVC ratio low: = obstructive defect.
FVC may be decreased in obstructive defect or normal

FVC low AND FEV1/FVC normal: restrictive defect, lost lung volume

FVC normal AND FEV1/FVC low: obstructive defect

FVC low AND FEV1/FVC low: obstructive defect, may be concomitant restriction. Need lung volumes (TLC, FRC, RV) to be sure

Question 6

What is indicative of gas trapping?

Answer 6

Elevated RV (and possibly FRC)

Question 7

What are indications for hyperinflation?

Answer 7

High RV, maybe FRC (gas trapping), maybe high TLC.

Question 8

What is diffusion capacity?

Answer 8

Severity judged like FEV1
Looks at functioning alveolar units, mostly sensitive to blood exposed to alveolar gas (ΘVc component) – i.e. capillary volume
Very sensitive to destruction of lung parenchyma and/or obliteration of vasculature
Often the earliest indicator of interstitial disease